Such clearance and speed controllers are also designated as ACC systems (adaptive cruise control) and they typically have a radar sensor as the sensor system, by which the clearances and relative speeds of preceding vehicles can be measured. In this way it is possible to follow a directly preceding vehicle, the so-called target object, at a suitable distance or, more accurately, at a suitably selected time gap. In clear-lane mode, when no target object is present, regulation takes place to a setpoint speed that is given, for instance, by a desired speed selected by the driver.
Examples of specified control parameters are setpoint speed, as well as the “dynamics” which are characterized, for instance, by the upper limits for the amount of the vehicle's acceleration and deceleration that are admissible in closed-loop regulation.
The ACC systems in use up to now are generally provided for travel on superhighways or well-improved country roads, and can only be activated above a certain minimum speed of 30 km/h, for example.
There are, however, ACC systems under development that have a broader functional scope, and they offer the following additional functions, for example: Travel following a preceding vehicle at very low speeds (below 30 km/h), braking to a standstill when the vehicle ahead stops, automatic holding of the vehicle at a standstill, and possibly, an automatic start-up again when traffic permits. An acoustical startup indication for the driver may then precede the startup process, if necessary. This broadened functionality is often collectively designated as a stop & go function.
Telematics systems are known, for the improvement of traffic flow, by which traffic jams in the highway network are automatically detected and can be reported to a traffic control center. German patent documents DE 199 17 154, DE 101 26 872 and DE 196 06 258 discuss, in this connection, traffic jam detection systems, which are installed onboard of vehicles of a so-called random sample fleet, and which are in a position to detect a traffic jam situation with the aid of the speed profile of their own vehicle. According to DE 196 06 258, the speed of the vehicle is continuously recorded and is classified according to specified speed classes. The classification result is then submitted to an integration process over time, and from the integration result, with the aid of fuzzy logic, a probability value is calculated for the presence of a traffic jam situation.